Abstract

The precedence effect (PE) describes the ability to localize a direct, leading sound correctly when its delayed copy (lag) is present, though not separately audible. The relative contribution of binaural cues in the temporal fine structure (TFS) of lead–lag signals was compared to that of interaural level differences (ILDs) and interaural time differences(ITDs) carried in the envelope. In a localization dominance paradigm participants indicated the spatial location of lead–lag stimuli processed with a binauralnoise-band vocoder whose noise carriers introduced random TFS. The PE appeared for noise bursts of 10 ms duration, indicating dominance of envelope information. However, for three test words the PE often failed even at short lead–lag delays, producing two images, one toward the lead and one toward the lag. When interaural correlation in the carrier was increased, the images appeared more centered, but often remained split. Although previous studies suggest dominance of TFS cues, no image is lateralized in accord with the ITD in the TFS. An interpretation in the context of auditory scene analysis is proposed: By replacing the TFS with that of noise the auditory system loses the ability to fuse lead and lag into one object, and thus to show the PE.

Received 09 July 2009Revised 09 November 2010Accepted 23 November 2010Published online 09 March 2011

Acknowledgments:

We thank the subjects for their participation and Ruth Litovsky, Wes Grantham, Ian Wiggins, and one anonymous reviewer for their suggestions toward improving this manuscript. Oliver Zobay helped with the statistical analysis (ANOVAs). This work was funded by National Institutes of Health RO1 DCD 00087 and the first author was supported by the Intramural Programme of the Medical Research Council (UK) during data analysis and write-up of the manuscript.

Article outline:I. INTRODUCTIONII. METHODSA. Subjects and stimuliB. Binaural stimuli with and without noise-band vocodingC. Localization testsD. PE test proceduresIII. EXPERIMENT 1: PE IN THE VIRTUAL FREE-FIELDA. Overview and proceduresB. ResultsIV. EXPERIMENT 2: PE WITH A NOISE-BAND VOCODERA. Overview and proceduresB. Results with low-pass and wide-band noise burstsC. Results with the word “shape”D. Results with the words “wide” and “teak”V. EXPERIMENT 3: THE PE DOES NOT FAIL COMPLETELYA. Overview and proceduresB. ResultsVI. ANALYSIS OF THE EFFECT OF VOCODINGVII. OVERALL DISCUSSIONA. Evaluation of binaural cuesB. Onset and duration effectsC. Influence of TFS and interaural coherenceD. A failure of auditory grouping?VIII. CONCLUSIONS